Network device, terminal device and methods for facilitating handover of terminal device

ABSTRACT

Methods implemented in a network device and a terminal device for facilitating handover of the terminal device served by the network device to a target beam and/or network device. The method in the network device comprises transmitting information on configurations for a set of candidate target beams and/or network devices to the terminal device before the handover of the terminal device is triggered. The method further comprises transmitting a handover command to the terminal device to trigger the handover of the terminal device. The handover command contains an identifier for identifying, from the transmitted information on the configurations for the candidate target beams and/or network devices, the information on the configuration for the target beam and/or network device. The disclosure also provides a network device and a terminal device that perform the above methods respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National stage of International Application No.PCT/CN2016/078296, filed Apr. 1, 2016, which is hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure generally relates to the technical field ofwireless communications, and particularly, to a network device, aterminal device and methods respectively implemented in the networkdevice and the terminal device for facilitating handover of the terminaldevice served by the network device to a target beam and/or networkdevice.

BACKGROUND

This section is intended to provide a background to the variousembodiments of the technology described in this disclosure. Thedescription in this section may include concepts that could be pursued,but are not necessarily ones that have been previously conceived orpursued. Therefore, unless otherwise indicated herein, what is describedin this section is not prior art to the description and/or claims ofthis disclosure and is not admitted to be prior art by the mereinclusion in this section.

To improve the throughput of wireless communication systems so as toprovide high-speed data services to a large amount of terminal devices,it has been proposed to employ a frequency spectrum which is much higherthan those where conventional systems (such as the 2^(nd)-4^(th) (2G-4G)systems) are deployed. At such a spectrum (in the order of tens of GHz,for example), the atmospheric attenuation, penetration and diffractionproperties of electromagnetic waves are much worse than at relativelylower frequencies. In addition, the link budget would be worse for thesame link distance even in a free space scenario. This motivates the useof beamforming to concentrate the energy of transmitted wireless signalsto compensate for the loss of link budget in high-frequency spectrum.

SUMMARY

As a result of the above described radio propagation properties andbeamforming, the radio coverage area offered by a network device inhigh-frequency wireless communication systems would be much smaller thanin existing low-frequency systems. Together with the limited ability forthe radio waves at the concerned frequencies to diffract, this makessudden loss of coverage of its serving network device a potentially muchmore frequent event to a moving terminal device.

Thus, a terminal device has to be handed over to a new beam and/ornetwork device when its current serving beam can no longer provide thecoverage it needs, and the terminal device can only know which beamand/or network device to connect to and how to connect to the targetbeam and/or network device during a handover procedure via a HO commandreceived from its serving network device.

Such a HO command is a bit large in size as it includes all necessaryinformation to tell the terminal device how to connect to a target beamand/or network device (hereinafter referred to as information onconfiguration for the target beam and/or network device). Accordingly,the transmission of the HO command is relatively time consuming and noteasy to protect (for example, through the use of Forward ErrorCorrection (FEC) encoding). Moreover, because the HO command isvulnerable to transmission error as explained above, there is a higherrisk that the terminal device does not successfully receive the HOcommand from its serving network device and thus cannot know which beamand/or network device to connect to and how to connect thereto.Accordingly, it has to detect a new network device from scratch and theoverall recover procedure takes a relatively long time.

In general, embodiments of the present disclosure provide solutions forfacilitating handover of a terminal device served by a network device toa target beam and/or network device.

According to a first aspect of the present disclosure, there is provideda method in a network device for facilitating handover of a terminaldevice served by the network device to a target beam and/or networkdevice. The method includes transmitting information on configurationsfor a set of candidate target beams and/or network devices to theterminal device before the handover of the terminal device is triggered.The method further includes transmitting a handover command to theterminal device to trigger the handover of the terminal device. Thehandover command contains an identifier for identifying, from thetransmitted information on the configurations for the candidate targetbeams and/or network devices, the information on the configuration forthe target beam and/or network device.

With the proposed solution, information on configurations for allcandidate target beams and/or network devices is transmitted to theterminal device indicating how to connect to the respective candidatetarget beams and/or network devices, before a handover commandcontaining an identifier is transmitted to the terminal deviceidentifying, from the transmitted configuration information, thespecific part for the actual target beam and/or network device of theterminal device. As such, the information on the configuration for theactual target beam and/or network device can be omitted from the HOcommand. Accordingly, the HO command is significantly reduced in size ascompared with the existing HO command which contains not only anidentifier of but also detailed configuration information for the actualtarget beam and/or network device of the terminal device as describedabove. Moreover, the transmission of the configuration information forthe actual target beam and/or network device as well as other candidatetarget beam and/or network device is reliable, as it occurs when thereis a good connection between the terminal device and its serving networkdevice and the handover of the terminal device is not triggered yet.

In an embodiment, the information on the configurations for thecandidate target beams and/or network devices may be stored in a tablewith indexes each uniquely identifying, from the table, an entrycontaining information on a respective one of the configurations for thecandidate target beams and/or network devices. The identifier foridentifying the information on the configuration for the target beamand/or network device may be one of the indexes which identifies anentry containing the information on the configuration for the targetbeam and/or network device.

In an embodiment, the indexes may be generated from identifiers of thecandidate target beams and/or network devices, respectively.

In an embodiment, the set of candidate target beams and/or networkdevices may include some or all of neighboring beams and/or networkdevices of the terminal device's serving beam and/or network device.

In an embodiment, the information on the configurations for the set ofcandidate target beams and/or network devices may be transmitted to theterminal device immediately after the terminal device connects to itsserving beam and/or network device.

In an embodiment, the information on the configurations for the set ofcandidate target beams and/or network devices may be transmitted to theterminal device when communication quality between the terminal deviceand its serving beam and/or network device falls down below a threshold.

In an embodiment, the method may further include stopping MobileReference Signal (MRS) transmissions from the serving network device andfrom all the set of candidate target beams and/or network devices exceptthe target beam and/or network device after the handover command istransmitted and requiring only the target beam and/or network device totransmit a MRS for a predetermined time period after the handovercommand is transmitted, so that the identifier for identifying theinformation on the configuration for the target beam and/or networkdevice is derivable at the terminal device from the MRS transmitted viathe target beam and/or network device and received by the terminaldevice.

According to a second aspect of the present disclosure, there isprovided a method in a terminal device for facilitating handover of theterminal device served by its serving network device to a target beamand/or network device. The method includes receiving information onconfigurations for a set of candidate target beams and/or networkdevices from the serving network device before the handover of theterminal device is triggered. The method further includes identifying,from the received information on the configurations for the candidatetarget beams and/or network devices, information on a configuration forthe target beam and/or network device, based on a received or derivedidentifier for the information on the configuration for the target beamand/or network device.

In an embodiment, the method may further include receiving from theserving network device a handover command that triggers the handover ofthe terminal device, wherein the handover command contains theidentifier for the information on the configuration for the target beamand/or network device.

In an embodiment, the method may further include receiving a MRS fromthe target beam and/or network device for a predetermined time periodwhile no MRS is received from the serving beam and/or network device orother candidate target beams and/or network devices among the set ofcandidate target beams and/or network devices during the time period.Then, the identifier for the information on the configuration for thetarget beam and/or network device is derived from the MRS received fromthe target beam and/or network device.

According to a third aspect of the present disclosure, there is provideda network device for facilitating handover of a terminal device servedby the network device to a target beam and/or network device. Thenetwork device includes a generating unit and a transceiving unit. Thegenerating unit is configured to generate information on configurationsfor a set of candidate target beams and/or network devices transmittedto the terminal device before the handover of the terminal device istriggered. The generating unit is further configured to generate ahandover command transmitted to the terminal device to trigger thehandover of the terminal device. The handover command contains anidentifier for identifying, from the transmitted information on theconfigurations for the candidate target beams and/or network devices,the information on the configuration for the target beam and/or networkdevice. The transceiving unit is configured to transmit the informationon configurations for the set of candidate target beams and/or networkdevices and the handover command to the terminal device.

According to a fourth aspect of the present disclosure, there isprovided a terminal device for facilitating handover of the terminaldevice served by its serving network device to a target beam and/ornetwork device. The terminal device includes a transceiving unit and anidentifying unit. The transceiving unit is configured to receiveinformation on configurations for a set of candidate target beams and/ornetwork devices from the serving network device before the handover ofthe terminal device is triggered. The identifying unit is configured toidentify, from the received information on the configurations for thecandidate target beams and/or network devices, information on aconfiguration for the target beam and/or network device, based on areceived or derived identifier for the information on the configurationfor the target beam and/or network device.

In an embodiment, the transceiving unit may be further configured toreceive from the serving network device a handover command that triggersthe handover of the terminal device, wherein the handover commandcontains the identifier for the information on the configuration for thetarget beam and/or network device.

In an embodiment, the transceiving unit may be further configured toreceive a MRS from the target beam and/or network device for apredetermined time period while no MRS is received from the serving beamand/or network device or other candidate target beams and/or networkdevices among the set of candidate target beams and/or network devicesduring the time period. The terminal device may further include aderiving unit configured to derive the identifier for the information onthe configuration for the target beam and/or network device from the MRSreceived from the target beam and/or network device.

According to a fifth aspect of the present disclosure, there is provideda network device for facilitating handover of a terminal device servedby the network device to a target beam and/or network device. Thenetwork device includes a memory and a processor. The memory hasmachine-readable instructions stored therein. The processor executes thestored machine-readable instructions to control the network device toperform the method according to the first aspect of the presentdisclosure.

According to a sixth aspect of the present disclosure, there is provideda terminal device for facilitating handover of the terminal deviceserved by its serving network device to a target beam and/or networkdevice. The terminal device includes a method and a processor. Thememory has machine-readable instructions stored therein. The processorexecutes the stored machine-readable instructions to control theterminal device to perform the method according to the second aspect ofthe present disclosure.

According to a seventh aspect of the present disclosure, there isprovided a computer program product including a non-transitory computerreadable storage medium storing therein executable instructionsconfigured to implement a method according to the first aspect or thesecond aspect of the disclosure.

According to an eighth aspect of the present disclosure, there isprovided a method performed in a wireless communication network forfacilitating handover of a terminal device served by its serving networkdevice to a target beam and/or network device. The method includesinitiating, by a handover control unit, transmission of a handovercommand to the terminal device to trigger the handover of the terminaldevice. Information on configurations for a set of candidate targetbeams and/or network devices have been transmitted to the terminaldevice before the handover of the terminal device is triggered. Thehandover command contains an identifier for identifying, from thetransmitted information on the configurations for the candidate targetbeams and/or network devices, the information on the configuration forthe target beam and/or network device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more fully apparent from the followingdescriptions on embodiments of the present disclosure with reference tothe drawings, in which like reference numerals or letters are used todesignate like or equivalent elements and in which:

FIG. 1 is a diagram illustrating a first handover scenario where aterminal device is handed over between beams from the same networkdevice;

FIG. 2 is a diagram illustrating a second handover scenario where aterminal device is handed over between beams from different networkdevices;

FIG. 3 is a diagram illustrating a third handover scenario where aterminal device is handed over between different network devices eachperforming transmission in an omnidirectional manner;

FIG. 4 is a flowchart illustrating a method implemented in a networkdevice for facilitating handover of a terminal device served by anetwork device to a target beam and/or network device according to thepresent disclosure;

FIGS. 5-7 are flowcharts illustrating a method implemented in a terminaldevice for facilitating handover of a terminal device served by anetwork device to a target beam and/or network device according to thepresent disclosure;

FIG. 8 is a diagram schematically an example of how a terminal deviceand its serving network device cooperate with each other to facilitatehandover of the terminal device according to the present disclosure;

FIG. 9 is a block diagram illustrating an exemplary functional structureof a network device according to the present disclosure;

FIG. 10 is a block diagram illustrating an exemplary software-basedimplementation of a network device according to the present disclosure;

FIG. 11 is a block diagram illustrating an exemplary functionalstructure of a terminal device according to the present disclosure;

FIG. 12 is a block diagram illustrating an exemplary software-basedimplementation of a terminal device according to the present disclosure;

FIG. 13 is a schematic diagram illustrating an exemplary implementationwherein functions of the network device described in conjunction withFIGS. 9 and 10 are performed by a single network device within awireless network; and

FIG. 14 is a schematic diagram illustrating an alternativeimplementation wherein functions of the network device described inconjunction with FIGS. 9 and 10 are distributed over two network deviceswithin a wireless network.

The drawings are illustrated for facilitating better understanding ofthe embodiments of the disclosure and not necessarily drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

In the discussion that follows, specific details of particularembodiments of the present disclosure are set forth for purposes ofexplanation and not limitation. It will be appreciated by those skilledin the art that other embodiments may be employed apart from thesespecific details. Furthermore, in some instances detailed descriptionsof well-known methods, nodes, interfaces, circuits, and devices areomitted so as not to obscure the description with unnecessary detail.Those skilled in the art will appreciate that the functions describedmay be implemented in one or in several nodes.

As used herein, the term “terminal device” refers to any end device thatcan access a wireless communication network and receive servicestherefrom. By way of example and not limitation, a terminal device maybe a user equipment (UE), which may be a Subscriber Station (SS), aPortable Subscriber Station, a Mobile Station (MS), or an AccessTerminal (AT). The mobile terminal may include, but is not limited to, amobile phone, a cellular phone, a smart phone, a tablet, a wearabledevice, a personal digital assistant (PDA), and the like.

The term “network device” refers to a device at the network side and mayinclude a network device via which a terminal device accesses thenetwork and receives services therefrom. By way of example, such anetwork device may be a base station (BS), a node B (NodeB or NB), anevolved NodeB (eNodeB or eNB), a Remote Radio Unit (RRU), a radio header(RH), a remote radio head (RRH), a relay, a low power node such as afemto, a pico, and so forth.

The terms “first” and “second” refer to different elements. The singularforms “a” and “an” are intended to include the plural forms as well,unless the context clearly indicates otherwise. The terms “comprises,”“comprising,” “has,” “having,” “includes” and/or “including” as usedherein, specify the presence of stated features, elements, and/orcomponents and the like, but do not preclude the presence or addition ofone or more other features, elements, components and/or combinationsthereof. The term “based on” is to be read as “based at least in parton.” The term “one embodiment” and “an embodiment” are to be read as “atleast one embodiment.” The term “another embodiment” is to be read as“at least one other embodiment.” Other definitions, explicit andimplicit, may be included below.

Some or all of the functions described may be implemented using hardwarecircuitry, such as analog and/or discrete logic gates interconnected toperform a specialized function, Application Specific Integrated Circuits(ASICs), Programmable Logical Arrays (PLAs), etc. Likewise, some or allof the functions may be implemented using software programs and data inconjunction with one or more digital microprocessors or general purposecomputers. Where nodes that communicate using the air interface aredescribed, it will be appreciated that those nodes also have suitableradio communications circuitry. Moreover, the technology canadditionally be considered to be embodied entirely within any form ofcomputer-readable memory, including non-transitory embodiments such assolid-state memory, magnetic disk, or optical disk containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein.

Hardware implementations of the presently disclosed techniques mayinclude or encompass, without limitation, digital signal processor (DSP)hardware, a reduced instruction set processor, hardware (e.g., digitalor analog) circuitry including but not limited to application specificintegrated circuit(s) (ASIC) and/or field programmable gate array(s)(FPGA(s)), and (where appropriate) state machines capable of performingsuch functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer, processor, and controller may be employedinterchangeably. When provided by a computer, processor, or controller,the functions may be provided by a single dedicated computer orprocessor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

Note that, although systems utilizing beamforming are described in thebackground section, solutions proposed here may or may not be usedtogether with beamforming. In the former case, the proposed solutionsare applicable to a first handover scenario where the handover of aterminal device occurs between beams from the same network device or asecond handover scenario where the handover of a terminal device occursbetween beams from different network devices. In the latter case, theproposed solutions are applicable to a third handover scenario where thehandover of a terminal device occurs between different network devices.

By way of illustration, FIG. 1 depicts the first handover scenario,where beams 210 and 220 are transmitted from a network device 110 and aterminal device 300 is handed over from beam 210 to beam 220 as it movesfrom the coverage area of beam 210 to the coverage area of beam 220.FIG. 2 depicts the second handover scenario, where a beam 210 and a beam220 are respectively transmitted from a network device 110 and a networkdevice 120 and a terminal device 300 is handed over from beam 210 tobeam 220 as it moves from the coverage area of beam 210 and hencenetwork device 110 to the coverage area of beam 220 and hence networkdevice 120. FIG. 3 depicts the third handover scenario, where a networkdevice 110 and a network device 120 each serve a coverage area in anomnidirectional manner and a terminal device 300 is handed over fromnetwork device 110 to network device 120 as it moves from the coveragearea of network device 110 to the coverage area of network device 120.

To facilitate understanding, reference numbers in FIGS. 1-3 will be usedto denote corresponding elements when describing the proposed solutionsin detail.

FIG. 4 schematically illustrates a method 400 in a network device 110for facilitating handover of a terminal device 300 served by the networkdevice 110 to a target beam 220 and/or network device 120 according tothe present disclosure.

As illustrated, the method begins with block s410, at which informationon configurations for a set of candidate target beams and/or networkdevices is transmitted to the terminal device 300 before the handover ofthe terminal device 300 is triggered.

As used herein, the expression “a configuration for a candidate targetbeam and/or network device” specifies how to connect to the candidatetarget beam and/or network device, and needs to be known to the terminaldevice 300 for handover to the candidate target beam and/or networkdevice. By way of example, such a configuration may include but is notlimited to random access related configuration, such as at which timeand frequency to send a Physical Random Access Channel (PRACH) preamble,how to receive a Radio Access Response (RAR) from the network, is theRAR accompanied with a control channel or not, or blind detection isneeded to decode RAR, where is the Reference Signal (RS) located forRAR, what is the RS to be used for UE to transmit message 3.

In practical implementation, the set of candidate target beams and/ornetwork devices may include all neighboring beams and/or network devicesof the terminal device's serving beam 210 and/or network device 110. Theneighboring beams and/or network devices may be configured by Operationand Maintenance (O&M), for example.

To further reduce information to be communicated between the terminaldevice and its serving network device and hence the consumption oflimited radio resources available for communications therebetween, theset of candidate target beams and/or network devices may include some ofall the neighboring beams and/or network devices of the terminaldevice's serving beam 210 and/or network device 110.

In an implementation, the neighboring beams and/or network devicesincluded in the set of candidate target beams and/or network devices maybe selected from all the neighboring beams and/or network devicesaccording to a predicted moving track of the terminal device. Forexample, the terminal device may be mounted on a bus which sticks to apredetermined schedule and moves along a fixed route. In that case, theneighboring beams and/or network devices included in the set ofcandidate target beams and/or network devices may be selected as thosealong the route.

Alternatively or additionally, the beams and/or network devices includedin the set of candidate target beams and/or network devices may beselected from all the neighboring beams and/or network devices accordingto habits of the user of the terminal device and/or monitored qualitiesof the neighboring beams and/or network devices. For example, theterminal device may be used by a person who is used to taking exercisesin a park every morning. In that case, the neighboring beams and/ornetwork devices included in the set of candidate target beams and/ornetwork devices may be selected as those having coverage areas within oroverlapping the area of the park. As another example, the neighboringbeams and/or network devices included in the set of candidate targetbeams and/or network devices may be selected as those whose qualitiesare better than a threshold.

In case the specific handover scenario can be predicted by the servingnetwork device 110 according to whether beamforming is employed and acurrent location of the terminal device 300, the serving network device110 can selectively transmit the information on configurations for theset of candidate target beams and network devices, the information onconfigurations for the set of candidate target beams or the informationon configurations for the set of candidate target network devices to theterminal device 300 at block 410.

Specifically, in case the serving network device 110 determines that itsupports beamforming and that the terminal device is far from the edgeof its coverage area, then it can predict the specific handover scenarioas the first handover scenario described above. In that case, theserving network device 110 only needs to transmit the information onconfigurations for the set of candidate target beams to the terminaldevice 300 at block s410.

In case the serving network device 110 determines that its neighboringnetwork devices and itself support beamforming and that the terminaldevice is near the edge of its coverage area, then it can predict thespecific handover scenario as the second handover scenario describedabove. In that case, the serving network device 110 has to transmit theinformation on configurations for the set of candidate target beams andnetwork devices to the terminal device 300.

In case the serving network device 110 determines that its neighboringnetwork devices and itself do not support beamforming and that theterminal device is near the edge of its coverage area, then it canpredict the specific handover scenario as the third handover scenariodescribed above. In that case, the serving network device only needs totransmit the information on configurations for the set of candidatetarget beams to the terminal device 300.

In practical implementation, the information on the configurations forthe set of candidate target beams and/or network devices may betransmitted to the terminal device 300 immediately after the terminaldevice connects to its serving beam 210 and/or network device 110.

Alternatively, the information on the configurations for the set ofcandidate target beams and/or network devices may be transmitted to theterminal device 300 when communication quality between the terminaldevice and its serving beam 210 and/or network device 110 falls downbelow a threshold (denoted as T1). Supposing the handover of theterminal device is triggered when the communication quality between theterminal device and its serving beam 210 and/or network device 110 fallsdown below a threshold (denoted as T2), T1 should be higher than T2.

Referring back to FIG. 4, after block s410, a handover command istransmitted to the terminal device 300 at block s420 to trigger thehandover of the terminal device 300. The handover command contains anidentifier for identifying, from the transmitted information on theconfigurations for the candidate target beams and/or network devices,the information on the configuration for the target beam 220 and/ornetwork device 120.

By way of example and not limitation, the identifier of the target beam220 and/or network device 120 may be used as the identifier contained inthe handover command.

In practical implementation, the information on the configurations forthe candidate target beams and/or network devices may be stored in atable with indexes each uniquely identifying, from the table, an entrycontaining information on a respective one of the configurations for thecandidate target beams and/or network devices. In this case, theidentifier for identifying the information on the configuration for thetarget beam 220 and/or network device 120 may be one of the indexeswhich identifies an entry containing the information on theconfiguration for the target beam 220 and/or network device 120.

As well known to those skilled in the art, a table refers to atwo-dimensional data structure that stores data elements in rows andcolumns. In case the information on the configurations for the candidatetarget beams and/or network devices is stored in a table, theconfiguration for each candidate target beam and/or network device maybe stored in a respective row of the table, and the values of the sameitem (for example, at which time and frequency to send a Physical RandomAccess Channel (PRACH) preamble) of the configurations for the candidatetarget beams and/or network devices may be stored in a respective columnof the table.

By way of example and not limitation, the indexes may be generated fromidentifiers of the candidate target beams and/or network devices,respectively.

As those skilled in the art will appreciate, any other data structuremay be used instead of a table, as long as it can carry theconfiguration information for all candidate target beams and/or networkdevices.

With the proposed method, information on configurations for allcandidate target beams and/or network devices is transmitted to theterminal device indicating how to connect to the respective candidatetarget beams and/or network devices, before a handover commandcontaining an identifier is transmitted to the terminal deviceidentifying, from the transmitted configuration information, thespecific part for the actual target beam and/or network device of theterminal device.

As such, the information on the configuration for the actual target beamand/or network device can be omitted from the HO command. Accordingly,the HO command is significantly reduced in size as compared with theprior art HO command which contains not only an identifier of but alsodetailed configuration information for the actual target beam and/ornetwork device of the terminal device. Accordingly, the HO command canbe transmitted in a shorter time period with higher reliability.

Moreover, the transmission of the configuration information for theactual target beam and/or network device as well as other candidatetarget beam and/or network device is reliable, as it occurs when thereis a good connection between the terminal device and its serving networkdevice and the handover of the terminal device is not triggered yet.

In an embodiment, the method 400 may further comprise block s430 shownin dashed block in FIG. 4. At this block, the serving network device 110stops Mobile Reference Signal (MRS) transmissions from the servingnetwork device 110 and from all the set of candidate target beams and/ornetwork devices except the target beam 220 and/or network device 120after the handover command is transmitted and requires only the targetbeam and/or network device to transmit a MRS for a predetermined timeperiod after the handover command is transmitted, so that the identifierfor identifying the information on the configuration for the target beam220 and/or network device 120 is derivable at the terminal device fromthe MRS transmitted via the target beam and/or network device andreceived by the terminal device.

In this manner, even if the terminal device 300 fails to receive thehandover command transmitted by its serving network device 110 at blocks420 due to poor communication quality therebetween, it can derive fromthe received MRS an identifier for identifying, from the receivedconfiguration information for all candidate target beams and/or networkdevices, the specific part for the actual target beam 220 and/or networkdevice 120. As a result, the risk of handover failure is reduced.

Correspondingly to the above-described method 400 implemented in aterminal device's serving network device, the present disclosureprovides a method 500 implemented in the terminal device forfacilitating handover of the terminal device to a target beam and/ornetwork device.

As illustrated in FIG. 5, the method 500 begins with block s510, atwhich information on configurations for a set of candidate target beamsand/or network devices is received from the serving network device 110before the handover of the terminal device 300 is triggered. After blocks510, information on a configuration for the target beam 220 and/ornetwork device 120 is identified at block s550 from the receivedinformation on the configurations for the candidate target beams and/ornetwork devices, based on a received or derived identifier for theinformation on the configuration for the target beam 220 and/or networkdevice 120.

In an embodiment, the method 500 may further comprise block s520 asillustrated in FIG. 6. At this block, the terminal device 300 receivesfrom the serving network device 110 a handover command that triggers thehandover of the terminal device 300. The handover command contains theidentifier for the information on the configuration for the target beam220 and/or network device 120.

In another embodiment, the method 500 may further comprise blocks s530and s540 as illustrated in FIG. 7. At block s530, the terminal device300 receives a MRS from the target beam and/or network device for apredetermined time period while no MRS is received from the serving beamand/or network device or other candidate target beams and/or networkdevices among the set of candidate target beams and/or network devicesduring the time period. At block s540, the terminal device 300 derivesthe identifier for the information on the configuration for the targetbeam 220 and/or network device 120 from the MRS received from the targetbeam and/or network device.

To facilitate understanding, FIG. 8 presents an example of how theserving network device 110 and the terminal device 300, which performthe above-described methods 400 and 500 respectively, cooperate witheach other to facilitate handover of the terminal device 300. For thesake of simplicity, the example is described with respect to theabove-described third handover scenario, where the network device 110and the network device 120 each serve a coverage area in anomnidirectional manner and the terminal device 300 is handed over fromnetwork device 110 to network device 120 as it moves from the coveragearea of network device 110 to the coverage area of network device 120.

As illustrated in FIG. 8, at step s810, the serving network device 110transmits information on configurations for a set of candidate targetnetwork devices to the terminal device 300. By way of example, the setof candidate target network devices include all neighboring networkdevices of the terminal device's serving network device 110, and theinformation on the configurations for the candidate network devices isstored in a table with indexes.

Upon detecting that communication quality between the terminal device300 and the serving network device 110 is lower than a threshold at steps820, the serving network device 10 transmits a handover command to theterminal device 300 at step s830. The handover command contains anidentifier for identifying, from the transmitted information on theconfigurations for the candidate target network devices, the informationon the configuration for the target network device 120. In case theinformation on the configurations for the candidate network devices isstored in a table with indexes, the identifier contained in the handovercommand may be one of the indexes which corresponds to the targetnetwork device 120.

In addition, at step s840 which is performed in serial or in parallelwith step s830, the serving network device 110 stops MRS transmissionafter the handover command is transmitted and requires only the targetnetwork device 120 among the set of candidate target network devices totransmit a MRS for a predetermined time period (denoted as t) after thehandover command is transmitted, so that the identifier for identifyingthe information on the configuration for the target network device 120is derivable at the terminal device 300 from the MRS transmitted via thetarget network device 120 and received by the terminal device 300.

In response, at step s850, the terminal device 300 identifies, from theinformation on the configurations for the candidate target beams and/ornetwork devices received at step s810, information on a configurationfor the target network device 120, based on a received or derivedidentifier for the information on the configuration for the targetnetwork device 120. Finally, at step s860, the terminal device 300connects to the target node 120 according to the identified informationon a configuration for the target network device 120.

In the following, exemplary functional structures and software-basedimplementations of a network device 110 and a terminal device 300according to the present disclosure will be given with reference toFIGS. 9-12.

As shown in FIG. 9, the network device 110 includes a generating unit1101 and a transceiving unit 1102. The generating unit 1101 isconfigured to generate information on configurations for a set ofcandidate target beams and/or network devices transmitted to theterminal device 300 before the handover of the terminal device 300 istriggered. The generating unit 1101 is further configured to generate ahandover command transmitted to the terminal device 300 to trigger thehandover of the terminal device 300. The handover command contains anidentifier for identifying, from the transmitted information on theconfigurations for the candidate target beams and/or network devices,the information on the configuration for the target beam 220 and/ornetwork device 120. The transceiving unit 1102 is configured to transmitthe information on configurations for the set of candidate target beamsand/or network devices and the handover command to the terminal device300.

In an embodiment, the information on the configurations for thecandidate target beams and/or network devices may be stored in a tablewith indexes each uniquely identifying, from the table, an entrycontaining information on a respective one of the configurations for thecandidate target beams and/or network devices. The identifier foridentifying the information on the configuration for the target beam 220and/or network device 120 may be one of the indexes which identifies anentry containing the information on the configuration for the targetbeam 220 and/or network device 120.

In an embodiment, the indexes may be generated from identifiers of thecandidate target beams and/or network devices, respectively.

In an embodiment, the set of candidate target beams and/or networkdevices may include all neighboring beams and/or network devices of theterminal device's serving beam 210 and/or network device 110.

In an embodiment, the set of candidate target beams and/or networkdevices may include some neighboring beams and/or network devices of theterminal device's serving beam 210 and/or network device 110, which areselected according to a predicted moving track of the terminal device.

In an embodiment, the information on the configurations for the set ofcandidate target beams and/or network devices may be transmitted to theterminal device 300 immediately after the terminal device connects toits serving beam 210 and/or network device 110.

In an embodiment, the information on the configurations for the set ofcandidate target beams and/or network devices may be transmitted to theterminal device 300 when communication quality between the terminaldevice and its serving beam 210 and/or network device 110 falls downbelow a threshold.

As those skilled in the art will appreciate, the above-described unitsmay be implemented separately as suitable dedicated circuits.Nevertheless, these units can also be implemented using any number ofdedicated circuits through functional combination or separation. In someembodiments, these units may be even combined in a single applicationspecific integrated circuit (ASIC).

As an alternative software-based implementation, there is provided anetwork device 110′ including a memory 1101′ and a processor 1102′(including but not limited to a microprocessor, a microcontroller or aDigital Signal Processor (DSP), etc.) as illustrated in FIG. 10. Thememory 1101′ stores machine-readable program code executable by theprocessor. The processor 1102′, when executing the machine-readableprogram code, controls the network device 110′ to perform theabove-described method 400.

Referring then to FIG. 11, the terminal device 300 includes atransceiving unit 3001 and an identifying unit 3002. The transceivingunit 3001 is configured to receive information on configurations for aset of candidate target beams and/or network devices from the servingnetwork device 110 before the handover of the terminal device 300 istriggered. The identifying unit 3002 is configured to identify, from thereceived information on the configurations for the candidate targetbeams and/or network devices, information on a configuration for thetarget beam 220 and/or network device 120, based on a received orderived identifier for the information on the configuration for thetarget beam 220 and/or network device 120.

In an embodiment, the transceiving unit 3001 may be further configuredto receive from the serving network device 110 a handover command thattriggers the handover of the terminal device 300, wherein the handovercommand contains the identifier for the information on the configurationfor the target beam 220 and/or network device 120.

In an embodiment, the transceiving unit 3001 may be further configuredto receive a MRS from the target beam and/or network device for apredetermined time period while no MRS is received from the serving beamand/or network device or other candidate target beams and/or networkdevices among the set of candidate target beams and/or network devicesduring the time period. The terminal device 300 may further comprise aderiving unit 3003 configured to derive the identifier for theinformation on the configuration for the target beam 220 and/or networkdevice 120 from the MRS received from the target beam and/or networkdevice.

As those skilled in the art will appreciate, the above-described unitsmay be implemented separately as suitable dedicated circuits.Nevertheless, these units can also be implemented using any number ofdedicated circuits through functional combination or separation. In someembodiments, these units may be even combined in a single applicationspecific integrated circuit (ASIC).

As an alternative software-based implementation, there is provided aterminal device 300′ including a transceiver 3001′, a processor 3002′(including but not limited to a microprocessor, a microcontroller or aDigital Signal Processor (DSP), etc.) coupled to the transceiver 3001′and a memory 3003′ as illustrated in FIG. 12. The transceiver 3001′ isfor bidirectional wireless communications and has at least one antennato facilitate communication. The memory 3003′ stores machine-readableprogram code executable by the processor 3002′. The processor 3002′,when executing the machine-readable program code, controls the terminaldevice 300′ to perform the above-described method 500.

FIG. 13 is a schematic diagram illustrating an exemplary implementationwherein functions of the network device 110/110′ described inconjunction with FIGS. 9 and 10 are performed by a single network device1300 within a wireless communication network.

Network Device 1300 may, in some embodiments, be an electronic devicebeing communicatively connected to other electronic devices on thenetwork (e.g., other network devices, end-user devices, radio basestations, etc.). In certain embodiments, a network device may includeradio access features that provide wireless radio network access toother electronic devices such as UEs. For example, network device 1300may be an eNodeB in Long Term Evolution (LTE) or other type of basestation as well as a radio network controller. Network device (ND) 1300may store and transmit (internally and/or with other electronic devicesover a network) code (which is composed of software instructions andwhich is sometimes referred to as computer program code or a computerprogram) and/or data using non-transitory machine-readable media (alsocalled computer-readable media), such as machine-readable storage media(e.g., magnetic disks, optical disks, read only memory (ROM), flashmemory devices, phase change memory) and machine-readable transmissionmedia (also called a carrier) (e.g., electrical, optical, radio,acoustical or other form of propagated signals—such as carrier waves,infrared signals). As depicted, network device 1300 includes a processor1301, a memory 1302, an interface 1303 and an antenna 1304. Thesecomponents may work together to provide various network devicefunctionality as disclosed hereinabove. Such functionality may includeimplementing all, or a portion, of the modules depicted in FIG. 13.

The components of the network device 1300 are depicted as single boxeslocated within a single larger box for reasons of simplicity indescribing certain aspects and features disclosed herein. In practicehowever, the network device 1300 may include multiple different physicalcomponents that make up a single illustrated component (e.g., theinterface 1303 may comprise terminals for coupling wires for a wiredconnection and a radio transceiver for a wireless connection). Asanother example, the network device 1300 may be a virtual network devicein which multiple different physically separate components interact toprovide the functionality of network device 1300 (e.g., processor 1301may comprise three separate processors located in three separateenclosures, where each processor is responsible for a different functionfor a particular instance of radio access network device 1300).Alternatively, the same physical components may be used to implementmultiple separate instances of the network device (e.g., processor 1301may execute separate instructions for multiple different instances of aradio access network device). Similarly, network device 1300 may becomposed of multiple physically separate components (e.g., a NodeBcomponent and a Radio Network Controller (RNC) component, a BaseTransceiver Station (BTS) component and a Base Station Controller (BSC)component, etc.), which may each have their own respective processor,storage, and interface components. These components may be dedicatedcomponents or they may be shared in a virtualized context. In certainscenarios in which network device 1300 includes multiple separatecomponents (e.g., BTS and BSC components), one or more of the separatecomponents may be shared among several network devices. For example, asingle RNC may control multiple NodeB's. In such a scenario, each uniqueNodeB and BSC pair, may be a separate network device. In someembodiments, network device 1300 may be configured such that somecomponents may be duplicated (e.g., separate memory 1302 for differentvirtual instances) and some components may be reused (e.g., the sameantenna 1304 may be shared by any and all virtual instances).

Processor 1301 may be a combination of one or more of a microprocessor,controller, microcontroller, central processing unit, digital signalprocessor, application specific integrated circuit, field programmablegate array, or any other suitable computing device, resource, orcombination of hardware, software and/or encoded logic operable toprovide, either alone or in conjunction with other network device 1300components, such as memory 1302.

Memory 1302 may comprise non-transitory machine readable storage media(also called computer-readable media) having stored therein software.For instance, memory 1302 may comprise non-volatile memory containingcode to be executed by processor 1301. Because memory 1302 isnon-volatile, the code and/or data stored therein can persist even whenthe network device is turned off (when power is removed). In someinstances, while the network device is turned on that part of the codethat is to be executed by the processor(s) may be copied fromnon-volatile memory into volatile memory (e.g., dynamic random accessmemory (DRAM), static random access memory (SRAM)) of that networkdevice.

Interface 1303 may be used in the wired or wireless communication ofsignaling and/or data to or from network device 1300. For example,interface 1303 may perform any formatting, coding, or translating thatmay be needed to allow network device 1300 to send and receive datawhether over a wired or a wireless connection. In some embodiments,interface 1303 may be coupled to one or more antennas 1304 which mayinclude one or more transceivers for communicating with other similarnetwork devices, with end user equipment and with other network devices.In some embodiments, interface 1303 may comprise radio circuitry thatmay receive digital data that is to be sent out to other network devicesvia a wireless connection. The radio circuitry may convert the digitaldata into a radio signal having the appropriate parameters (e.g.,frequency, timing, channel, bandwidth, etc.). The radio signal may thenbe transmitted via antennas 1304 to the appropriate recipient(s). Theradio circuitry of interface 1303 may in some instances comprisefunctionality for linking the Common Public Radio Interface (CPRI)stream and the antenna 1304.

The L1 module 1305 handles uplink and downlink in the physical layer,layer 1 of the protocol stack. In uplink, the L1 module processesantenna data received from the radio circuitry (e.g., over Common PublicRadio Interface (CPRI)), which data processing may include removingcyclic prefix, running Fast Fourier Transform (FFT) to extractsub-channels, decoding/demodulating symbols, extracting physicalchannels and passing user information up to the lower layer of L2 MediaAccess Control (MAC). In downlink, the L1 module takes user dataprovided by lower layer of L2 MAC. Examples of tasks that may beperformed by the L1 module in downlink may include constructing physicalchannels, performing turbo coding, scrambling, modulating, layermapping, pre-coding, frequency mapping, inverse FFT, and cyclic prefixinsertion and sending antenna data (e.g., over CPRI) to the interface1303. To handle this processing, specialized hardware may be used,including accelerators, to form processing chains.

The L2-Sync module 1306 includes the synchronous parts of layer 2 of theprotocol stack. The L2-Sync module includes the 3rd GenerationPartnership Project (3GPP) sub-layers Medium Access Control (MAC)(including Hybrid Automatic Repeat Request (HARQ)) and Radio LinkControl (RLC). The MAC sub-layer may have a separate HARQ entity foreach connected UE, and a few additional HARQ entities for common needssuch as system information, paging, and random access response. The RLCsub-layer may have a separate RLC entity for each logical channel,corresponding to radio bearers. Downlink and uplink may operateindependently of each other, with some signaling forwarded from theuplink to the downlink. Downlink: A task of the L2-Sync module indownlink may be to take Packet Data Convergence Protocol (PDCP) PacketData Units (PDUs) from a PDCP PDU buffer and build MAC PDUs that aresent to the L1 module. This may be triggered by a transmit order fromUser Plane Control (UPC) module. In downlink the L2-Sync module may alsohandle multiplexing of logical channels, HARQ retransmissions, MACcontrol elements, MAC procedures such as random access, RLC PDUbuffering and retransmissions, and RLC status messages. The PDCP PDUbuffers may typically be shared between the L2-Async module and theL2-Sync module. If this is not possible, for example, if L2-Async isplaced at a different site, a flow control mechanism may be added totransfer PDCP PDUs from the L2-Async module to the L2-Sync module.Uplink: A task of the L2-Sync module in uplink may be to deconstruct MACPDUs received from the L1 module into PDCP PDUs that are delivered tothe L2-Async module. In uplink the L2-Sync module may also handle MACcontrol elements, MAC procedures such as random access, demultiplexingof logical channels, RLC PDU buffering, reordering and retransmissions,and RLC status messages. In uplink the L2-Sync module may not be part ofa latency critical processing path, but may have a direct impact on theend-to-end packet latency.

The UPC (User Plane Control) module 1307 includes fast radio resourcemanagement (RRM) functions that may occur on a per-subframe basis. Thismay include air-interface resource scheduling, link adaptation(transport format selection), and power control. The UPC module may useinput from other modules such as the L1 module and the L2-Sync module,and generate messages to other modules such as the L1 module and theL2-Sync module. The input may include buffer status reports, measurementreports, Channel Quality Indicator (CQI) reports, and HARQ feedback. Themessages may be control information sent to the UEs, as well as uplinkand downlink scheduling commands sent to the L1 module and the L2-Syncmodule. The UPC module may thus handle scheduling and optimizationproblems, involving many UEs and shared resources such as spectrum,power, and hardware.

The L2-Async module 1308 includes the PDCP layer, whose primary tasksmay be ciphering, header compression, and integrity protection forsignaling. It may also support lossless handover. In downlink, L2-Asyncmodule may maintain a PDCP PDU buffer, which is often shared with theL2-Sync module when suitable, as discussed above.

The RRM-C (Radio Resource Management Coordination) module 1309, includesfunctions to coordinate multiple UPC instances. The RRM-C module mayinclude functions for performing one or more of the following:Coordinated Multipoint (CoMP) including fast and slow uplink/downlink,Combined Cell, Dual Connectivity, Inter-Cell Interference Coordination(ICIC), enhanced Inter-Cell Interference Coordination (eICIC) andFurther enhanced Inter-Cell Interference Coordination (FeICIC). TheRRM-C module may take input from the L1 and the L2-Async modules andgenerate messages to the UPC module.

The UEH (User Equipment Handler) module 1310, includes functions for thehandling and control of UE related control plane functions. UEH consistsof 3GPP sub-layer Radio Resource Control (RRC). This includes thecontrol of one or more of the following functions: Connection handling,such as setup and release of connections; Mobility handling, such ashandover or redirection release; UE Measurement Control; LoadManagement, such as Inter-Frequency Load Balancing and Offload; andEnhanced Multimedia Broadcast and Multicast Services (eMBMS). Thus, theUEH module 1310 plays a critical role in performing the above-describedmethod 400 which relates to handover. The UEH module may also implementthe application protocols for communication with a mobility managemententity (e.g. S1-AP, M3-AP) and other base stations (e.g. X2-AP). The UEHmodule may logically have a separate entity for each connected UE,storing all necessary data in a UE Context. Each separate entity mayalso implement the state machine for running all control-plane featuresrelated to a UE, including the necessary coordination between differentfunctions for a specific UE.

The RNH (Radio Network Handler) module 1311, includes functionality tomanage logical cells in the radio network on order from an operator. TheRNH module may also be responsible for the handling of LRAT specificconfiguration data on cell and node/device level. This also includes thehandling of cell relations and neighbor cell data, such as EvolvedUniversal Terrestrial Radio Access Network (EUTRAN) neighbor cells andcells belonging to other RATs. The RNH module may also implement anumber of Self-Organizing Network (SON) related functions such asautomatic handling of neighbor relations (ANR); X2 Handling, i.e.automatic handling of external base station and cells referencesreceived from another base station over an interface used forcommunication between base stations, such as X2; and Mobility RobustnessOptimization (MRO), i.e. automatic tuning of mobility relatedparameters.

The TN (Transport Network) module 1312, includes features for providingthe node/device with transport network capabilities based on InternetProtocol (IP) (both IPv4 and IPv6 hosts) for messages with forwardingand protocol termination. Examples of protocols could include StreamControl Transmission Protocol (SCTP), Transmission Control Protocol(TCP), User Datagram Protocol (UDP) and GPRS Tunneling Protocol UserPlane, (GTP-U), with support for Security, the protocols to be used overthe paths S1, M3, X2 and/or Mul. The TN module may handle the forwardingof TN traffic between Digital Units (DUs) (within the node/device andbetween node/devices) and management of Site Local Area Networks (LAN)packets forwarding to the Operations and Maintenance (OAM) system.Security may be supported with Internet Protocol Security (IPSec),including Internet Key Exchange (IKE) handling and Access control lists(ACL) for the Site LAN. The TN module may also handle shapingcapabilities for overload situations on the transport network whenneeded. The interaction between the transport and radio network makes itpossible for the radio domain to adapt to the actual resource situationin the backhaul network. This is done by extension in the transportnetwork domain, and an interface to the radio domain which makes itpossible for the transport network to report the available transportresources and characteristic for specific network path(s) requested bythe radio network domain. This can be the available S1 path(s) in thetransport network to the core network or X2 path(s) to neighboring cellsites.

As an alternative implementation to that illustrated in FIG. 13,functions of the network device 110/110′ described in conjunction withFIGS. 9 and 10 may be distributed over two network devices within awireless communication network as illustrated in FIG. 14.

As depicted, in addition to a network device 1400 which has the samestructure and modules as the network device 1300, another network device1500 separate from the network device 1400 also implements an UEH module1510 that cooperates with the UEH module 1410 in the network device 1400for controlling handover.

In such an implementation, the network device 1400 may be a servingnetwork device with which a terminal device may communicate directly soas to access the network and the network device 1500 may not communicatewith the terminal device directly but serves as a handover control unitwhich initiates transmission of a handover command from the networkdevice 1400 to the terminal device to trigger the handover of theterminal device. Information on configurations for a set of candidatetarget beams and/or network devices have been transmitted from thenetwork device 1400 to the terminal device before the handover of theterminal device is triggered. The handover command contains anidentifier for identifying, from the transmitted information on theconfigurations for the candidate target beams and/or network devices,the information on the configuration for the target beam and/or networkdevice.

In an embodiment, the network device 1500 which serves as the handovercontrol unit further stops Mobile Reference Signal (MRS) transmissionsfrom the serving network device and from all the set of candidate targetbeams and/or network devices except the target beam and/or networkdevice after the handover command is transmitted and requires only thetarget beam and/or network device among the set of candidate targetbeams and/or network devices to transmit a MRS for a predetermined timeperiod after the handover command is transmitted, so that the identifierfor identifying the information on the configuration for the target beamand/or network device is derivable at the terminal device from the MRStransmitted via the target beam and/or network device and received bythe terminal device.

The present disclosure is described above with reference to theembodiments thereof. However, those embodiments are provided just forillustrative purpose, rather than limiting the present disclosure. Thescope of the disclosure is defined by the attached claims as well asequivalents thereof. Those skilled in the art can make variousalternations and modifications without departing from the scope of thedisclosure, which all fall into the scope of the disclosure.

What is claimed is:
 1. A method in a network device for facilitatinghandover of a terminal device served by the network device to a targetbeam or to a target network device, the method comprising: transmittinginformation on configurations for a set of candidate target beams orcandidate target network devices, or both candidate target beams andcandidate target network devices, to the terminal device before thehandover of the terminal device is triggered; transmitting a handovercommand to the terminal device to trigger the handover of the terminaldevice, wherein the handover command contains an identifier foridentifying, from the transmitted information on the configurations forthe set of the candidate target beams or the candidate target networkdevices, or both, information on the configuration for the target beamor the target network device; and stopping Mobile Reference Signal (MRS)transmissions from the network device or a beam of the network deviceserving the terminal device and from the set of candidate target beamsor the candidate target network devices, or both, except the target beamor the target network device, after the handover command is transmittedand requiring only the target beam or the target network device totransmit a MRS for a predetermined time period after the handovercommand is transmitted, so that the identifier for identifying theinformation on the configuration for the target beam or the targetnetwork device is derivable at the terminal device from the MRStransmitted via the target beam or the target network device andreceived by the terminal device.
 2. The method of claim 1, wherein theinformation on the configurations for the set of the candidate targetbeams or the candidate target network devices, or both, is stored in atable with indexes each uniquely identifying, from the table, an entrycontaining information on a respective one of the configurations for theset of the candidate target beams or the candidate target networkdevices, or both, and the identifier for identifying the information onthe configuration for the target beam or the target network device isone of the indexes which identifies an entry containing the informationon the configuration for the target beam or the target network device.3. The method of claim 2, wherein the indexes are generated fromidentifiers of the set of the candidate target beams or the candidatetarget network devices, or both, respectively.
 4. The method of claim 1,wherein the set of the candidate target beams or the candidate targetnetwork devices, or both, includes some or all of neighboring beams orneighboring network devices, or both neighboring beams and neighboringnetwork devices, of the network device or a beam of the network deviceserving the terminal device.
 5. The method of claim 1, wherein theinformation on the configurations for the set of the candidate targetbeams or the candidate target network devices, or both, is transmittedto the terminal device immediately after the terminal device connects tothe network device or a beam of the network device serving the terminaldevice.
 6. The method of claim 1, wherein the information on theconfigurations for the set of the candidate target beams or thecandidate target network devices, or both, is transmitted to theterminal device when communication quality between the terminal deviceand the network device or a beam of the network device serving theterminal device falls down below a threshold.
 7. A method in a terminaldevice for facilitating handover of the terminal device served by aserving network device to a target beam or to a target network device,the method comprising: receiving information on configurations for a setof candidate target beams or candidate target network devices, or bothcandidate target beams and candidate target network devices, from theserving network device before the handover of the terminal device istriggered; identifying, from the received information on theconfigurations for the set of the candidate target beams or thecandidate target network devices, or both, information on aconfiguration for the target beam or the target network device, based ona received or derived identifier for the information on theconfiguration for the target beam or the target network device;receiving a Mobile Reference Signal (MRS) from the target beam or thetarget network device for a predetermined time period while MRStransmissions are not transmitted from the serving network device or abeam of the serving network device serving the terminal device, or othercandidate target beams or other candidate target network devices, orboth of the other candidate target beams and the other candidate targetnetwork devices, among the set of the candidate target beams or thecandidate target network devices, or both, during the predetermined timeperiod; and deriving the identifier for the information on theconfiguration for the target beam or the target network device from theMRS received from the target beam or the target network device.
 8. Themethod of claim 7, further comprising: receiving from the servingnetwork device a handover command that triggers the handover of theterminal device, wherein the handover command contains the identifierfor the information on the configuration for the target beam or thetarget network device.
 9. The method of claim 7, wherein the informationon the configurations for the set of the candidate target beams or thecandidate target network devices, or both, is stored in a table withindexes each uniquely identifying, from the table, an entry containinginformation on a respective one of the configurations for the set of thecandidate target beams or the candidate target network devices, or both,and the identifier for identifying the information on the configurationfor the target beam or the target network device is one of the indexeswhich identifies an entry containing the information on theconfiguration for the target beam or the target network device.
 10. Themethod of claim 9, wherein the indexes are generated from identifiers ofthe set of the candidate target beams or the candidate target networkdevices, or both, respectively.
 11. A network device for facilitatinghandover of a terminal device served by the network device to a targetbeam or to a target network device, the network device comprising: aprocessor and a non-transitory computer readable storage medium, thenon-transitory computer readable storage medium containing instructions,which when executed by the processor, cause the network device to:generate information on configurations for a set of candidate targetbeams or candidate target network devices, or both candidate targetbeams and candidate target network devices, for transmission to theterminal device before the handover of the terminal device is triggered;generate a handover command for transmission to the terminal device totrigger the handover of the terminal device, wherein the handovercommand contains an identifier for identifying, from the information onthe configurations for the set of the candidate target beams or thecandidate target network devices, or both, information on theconfiguration for the target beam or the target network device; transmitthe information on configurations for the set of the candidate targetbeams or the candidate target network devices, or both, and the handovercommand to the terminal device; and stop Mobile Reference Signal (MRS)transmission after the handover command is transmitted and to transmitan instruction instructing only the target beam or the target networkdevice among the set of the candidate target beams or the candidatetarget network devices, or both, to transmit a MRS for a predeterminedtime period after the handover command is transmitted, so that theidentifier for identifying the information on the configuration for thetarget beam or the target network device is derivable at the terminaldevice from the MRS transmitted via the target beam or the targetnetwork device and received by the terminal device.
 12. The networkdevice of claim 11, wherein the information on the configurations forthe set of the candidate target beams or the candidate target networkdevices, or both, is stored in a table with indexes each uniquelyidentifying, from the table, an entry containing information on arespective one of the configurations for the set of the candidate targetbeams or the candidate target network devices, or both, and theidentifier for identifying the information on the configuration for thetarget beam or the target network device is one of the indexes whichidentifies an entry containing the information on the configuration forthe target beam or the target network device.
 13. The network device ofclaim 12, wherein the indexes are generated from identifiers of the setof the candidate target beams or the candidate target network devices,or both, respectively.
 14. The network device of claim 11, wherein theset of the candidate target beams or the candidate target networkdevices, or both, includes some or all neighboring beams or neighboringnetwork devices, or both neighboring beams and neighboring networkdevices, of the network device or a beam of the network device servingthe terminal device.
 15. The network device of claim 11, wherein theinformation on the configurations for the set of the candidate targetbeams or the candidate target network devices, or both, is transmittedto the terminal device immediately after the terminal device connects tothe network device or a beam of the network device serving the terminaldevice.
 16. The network device of claim 11, wherein the information onthe configurations for the set of the candidate target beams or thecandidate target network devices, or both, is transmitted to theterminal device when communication quality between the terminal deviceand the network device or a beam of the network device serving theterminal device falls down below a threshold.
 17. A terminal device forfacilitating handover of the terminal device served by a serving networkdevice to a target beam or to a target network device, the terminaldevice comprising: a processor and a non-transitory computer readablestorage medium, the non-transitory computer readable storage mediumcontaining instructions, which when executed by the processor, cause theterminal device to: receive information on configurations for a set ofcandidate target beams or candidate target network devices, or bothcandidate target beams and candidate target network devices, from theserving network device before the handover of the terminal device istriggered; identify, from the received information on the configurationsfor the set of the candidate target beams or the candidate targetnetwork devices, or both, information on a configuration for the targetbeam or the target network device, based on a received or derivedidentifier for the information on the configuration for the target beamor the target network device; receive a Mobile Reference Signal (MRS)from the target beam or the target network device for a predeterminedtime period while MRS transmissions are not transmitted from the servingnetwork device or a beam of the serving network device serving theterminal device, or other candidate target beams or other candidatetarget network devices, or both of the other candidate target beams andthe other candidate target devices, among the set of the candidatetarget beams or the candidate target network devices, or both, duringthe predetermined time period; and derive the identifier for theinformation on the configuration for the target beam or the targetnetwork device from the MRS received from the target beam or the targetnetwork device.
 18. The terminal device of claim 17, wherein theinstructions further cause the terminal device to receive from theserving network device a handover command that triggers the handover ofthe terminal device, wherein the handover command contains theidentifier for the information on the configuration for the target beamor the target network device.
 19. The terminal device of claim 17,wherein the information on the configurations for the set of thecandidate target beams or the candidate target network devices, or both,is stored in a table with indexes each uniquely identifying, from thetable, an entry containing information on a respective one of theconfigurations for the set of the candidate target beams or thecandidate target network devices, or both, and the identifier foridentifying the information on the configuration for the target beam orthe target network device is one of the indexes which identifies anentry containing the information on the configuration for the targetbeam or the target network device.
 20. The terminal device of claim 19,wherein the indexes are generated from identifiers of the set of thecandidate target beams or the candidate target network devices, or both,respectively.
 21. A method performed in a wireless communication networkfor facilitating handover of a terminal device served by a servingnetwork device to a target beam or to a target network device, themethod comprising: initiating, by a handover control unit, transmissionof a handover command to the terminal device to trigger the handover ofthe terminal device, wherein information on configurations for a set ofcandidate target beams or candidate target network devices, or bothcandidate target beams and candidate target network devices, have beentransmitted to the terminal device before the handover of the terminaldevice is triggered; the handover command contains an identifier foridentifying, from the information on the configurations for the set ofthe candidate target beams or the candidate target network devices, orboth, information on the configuration for the target beam or the targetnetwork device; and initiating, by the handover control unit, stoppingof Mobile Reference Signal (MRS) transmissions from the serving networkdevice and from all the set of the candidate target beams or thecandidate target network devices, or both, except the target beam or thetarget network device, after the handover command is transmitted andrequiring only the target beam or the target network device to transmita MRS for a predetermined time period after the handover command istransmitted, so that the identifier for identifying the information onthe configuration for the target beam or the target network device isderivable at the terminal device from the MRS transmitted via the targetbeam or the target network device and received by the terminal device.